Glutaminase (glutaminase I, L-glutaminase, glutamine aminohydrolase) is an amido-hydrolase enzyme that generates glutamate from glutamine. Glutaminase has been reported to have tissue-specific isoenzymes. Glutaminase has an important role in glial cells. Glutamine is the most abundant free amino acid in the human body; it is essential for the growth of normal and neoplastic cells and for the culture of many cell types. Glutamine is an important source of energy for neoplastic tissues, and products of its metabolism include, among others, glutamate (Glu) and glutathione (GSH), the two molecules that play a key role in tumor proliferation, invasiveness and resistance to therapy. Glutamine hydrolysis in normal and transforming mammalian tissues alike is carried out by different isoforms of glutaminases, of which the two major types are liver-type glutaminase (LGA) and kidney-type glutaminase (KGA) (see Neurochem Int., 2009 July-August; 55(1-3):71-5. doi: 10.1016/j.neuint.2009.01.008. Epub 2009 February).
Cancer cells require a robust supply of reduced nitrogen to produce nucleotides, non-essential amino acids and a high cellular redox activity. Glutamine provides a major substrate for respiration as well as nitrogen for the production of proteins, hexosamines, and macromolecules. Therefore, glutamine is one of key molecules in cancer metabolism during cell proliferation. The notion of targeting glutamine metabolism in cancer, originally rationalized by the number of pathways fed by this nutrient, has been reinforced by more recent studies demonstrating that its metabolism is regulated by oncogenes. Glutaminase (GA) is the first enzyme that converts glutamine to glutamate, which is in turn converted to alpha-ketoglutarate for further metabolism in the tricarboxylic acid cycle. Different GA isoforms in mammals are encoded by two genes, Gls and Gls2. As each enzymatic form of GA has distinct kinetic and molecular characteristics, it has been speculated that the differential regulation of GA isoforms may reflect distinct functions or requirements in different tissues or cell states. GA encoded by the Gls gene (GLS) has been demonstrated to be regulated by oncogenes and to support tumor cell growth. GA encoded by the Gls2 gene (GLS2) reduces cellular sensitivity to reactive oxygen species associated apoptosis possibly through glutathione-dependent antioxidant defense, and therefore to behave more like a tumor suppressor. Thus, modulation of GA function may be a new therapeutic target for cancer treatment (see Matćs et al., Curr. Mol. Med., 2013 May; 13(4), 514-534).
One hallmark of cancer cells is their adaptation to rely upon an altered metabolic scheme that includes changes in the glycolytic pathway, known as the Warburg effect, and elevated glutamine metabolism. Glutaminase, a mitochondrial enzyme, plays a key role in the metabolism of glutamine in cancer cells, and its inhibition could significantly impact malignant transformation (see Katt et al., Mol. Cancer Ther., 11(6); 1269-78, 2012). Feeding off the breakdown of glutamine, cancer cells are able to grow and divide into a tumour. Glutaminase therefore makes a promising therapeutic target for the prevention of tumour progression. Inhibition of this enzyme could effectively starve the cancer cells of their energy source. See Medina et al., J. Nutr., Sep. 1, 2001, Vol. 131, No. 9 2539S-2542S.
Glutaminase plays a crucial role in the mechanisms of cancer, such as cell survival, proliferation and growth. There are two reported glutaminase inhibitors namely 6-diazo-5-oxo-L-norleucine (DON) which was isolated originally from Streptomyces in a sample of Peruvian soil and was characterized in 1956 by Henry W Dion (see Dion et al., Antibiotics and Chemotherapy, 1954, 78, 3075-3077) and suggested as a cancer therapy and bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES) disclosed by Elan Pharmaceuticals. There is an ongoing research effort reported by other groups working at Cornell University and Calithera Biosciencesis to discover and identify small molecule inhibitors of glutaminase. DON has also been reported to be evaluated in combination with PEG-PGA by New Medical Enzymes AG. In addition to BPTES and DON, other reported glutaminase inhibitors are as summarised in the table below.
AgentCompanyClinical statusBPTES—DiscoveryCB-839Calithera BiosciencesPhase-1Compound 968Cornell UniversityPreclinicalGlutaDONNew Medical EnzymesPhase-2(PEG-PGA + DON)AGGlutaChemoNew Medical EnzymesPreclinical(PEG-PGA + an ideal candidate)AG
Reviews and studies regarding Glutamine and Glutaminase in cancer and other discesase have been given by Medina et al., J. Nutr., Sep. 1, 2001, Vol. 131, No. 9, 2539S-2542S; Ajit G. Thmas et al., Biochemical and Biophysical Research Communications, 443, 2014, 32-36; Monica Szeliga et al., Neurochemistrt Intermationa, 55, 2009, 71-77; and Curthoys et al., Annu. Rev. Nutr., 1995, 15, 133-159. All of these literature disclosures are incorporated herein by reference in their entirety for all purposes.
Patent literature related to glutaminase inhibitors includes International Publication Nos. WO 99/09825, WO 00/59533, WO 03/022261, WO 04/108153, WO 07/128588, WO 10/033871, WO 10/111504, WO 11/076967, WO 11/143160, WO 12/006506, WO 12/034123, WO 13/044596, WO 13/078123, WO 14/078645, WO 14/089048, WO14/043633, WO14/079011, WO14/079136, WO14/079150, and WO14/081925, U.S. Publication Nos. 2002/0115698, 2006/0276438, 2013/0157998, 2014/0050699, 2014/0194421, 2014/0369961, 2015/0004134, 20140142081, and 20140142146, U.S. Pat. Nos. 5,552,427, 6,451,828, 8,465,736, 8,604,016, and 8,865,718 and European Publication No. 656210, each of which is incorporated herein by reference in its entirety for all purposes.
There still remains an unmet need for novel glutaminase inhibitors for the treatment of diseases and disorders associated with cell proliferation such as cancer and other immunological and neurological disorders.